1. Field of the Invention
This invention relates generally to an equalizer in which a coefficient is automatically controlled and, more particularly, to an automatically adaptive equalizer for use in a digital tape recorder or the like.
2. Description of the Background
In most known magnetic recording/reproducing apparatus, such as audio tape recorders, video tape recorders, or the like, the reproduced signal from the playback head is passed through an equalizer that has specifically selected frequency response characteristics. Generally, in such equalizers the high frequency range during playback is emphasized to compensate high-frequency signal loss caused by increased recording density. Typically, the frequency characteristics of this kind of equalizer are fixed once they are adjusted for the desired optimum performance. A problem arises, however, in that the frequency characteristics in the playback mode can change for various reasons. Among such reasons are the different types of tape being employed, tape aging, reproduction demagnetization, a change in spacing loss due to deterioration of the tape surface caused by repetitive playback and recording, variations in the characteristics of the head, a change in the rotary transformer caused by head wear, or a change in the gap dimension of the rotary transformer as a result of bearing wear, a variation in the azimuth angle of the playback and recording head from apparatus to apparatus, variations in the recording current, a change in the tape contact angle of the heads caused by a change in temperature or humidity, temperature characteristics, and overall aging of the electrical parts making up the circuitry of the tape recorder apparatus.
Therefore, even though many of the above changes in characteristics are generally minor, they do adversely affect the performance of the tape recorder so that the use of an equalizer that is permanently adjusted or fixed will not result in optimum performance or reliability. Furthermore, when the equalizer characteristics made to be adjustable within a particular tolerance band to take into consideration the variations in frequency characteristics caused by the various parameter changes described above, the recording density on the tape is adversely affected by this tolerance band.
Thus, elements whose values are adjustable are necessary for use, such as a potentiometer, a trimmer capacitor, or the like, in order to permit adjustment at the time of manufacture and for subsequent re-adjustment during maintenance procedures. The use of these additional parts increases the overall cost of the equipment and also results in higher labor costs and increases the overall bulk of the apparatus.